The feeding of the webs into a processing line, such as a winding system, after a start/restart of the production is a delicate process in particular for thin webs. A known method for such feeding is to cut off manually an edge or a leader of the web, to take it manually through the processing line, launching a defined start program, and when the edge or the leader is secured on a driving element, to cut the web in such a way that the entirety thereof is finally fed into the processing line.
It will be readily apparent that there is a need for an apparatus and a method that would offer a safe and easy cutting and feeding of the web into the processing line, and that would afford automatic thread up. This need is acute for films with thickness ranging from 100 to 0.4 microns and speeds up to 1000 m/min as well as widths ranging from 1 m to 10 m.
Said need exists for various types of material: polymeric, paper, metallic, etc. “Web” shall thus cover any of this material.
The method of the leader (either manually or automatically) is already known and exemplified in, e.g., U.S. Pat. Nos. 3,756,527 and 3,743,197. These patents teach the use of a single central leader strip that is inserted into the processing line; once said leader strip is secured the strip is broadened up to the full width of the web. The leader strip is transported pneumatically using a slotted tube. This, however, presents drawbacks. Because of the slots, it is not possible to build up a significant pressure gradient along the tube or channel; air speeds and consequently aerodynamic forces are limited. Pulling the leader strip out of the slots is a delicate operation, often ending in breaks with thin films. The tubes hinder the production because centrally located, along the whole line.
An alternate method using the edges present on both sides of the film or web is disclosed in U.S. Pat. No. 4,611,518. According to this document, the method makes use of said edges being first cut from the central part of the web, then fed into the processing line. The mechanism used for achieving this comprises pressure rolls, constituting a nip, which secures the edges, where the edges are then transported by a double belt (called rope scissors) through the machine. This, however, presents drawbacks. The edges can wrap around the pressure rolls, leading to downtime. The system is very complicated. Edge transport with pressure rolls and with a double belt is not convenient in the case of stretched polymeric films because the edge (aka bead) has then a non uniform thickness and may be corrugated and curled (as a result, the edge can get out sidewards).